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Thorax:Bones:Ribs
Typical ribs: * 12 pairs, symmetrically arrayed; numbered in accordance with attached vertebral body * True ribs (1-7) attach to sternum by costal cartilages (synovial joints) * False ribs (8-10) articulate by costal cartilages with costal cartilage of 7th rib * Floating ribs (11-12) do not articulate with sternum or rib costal cartilages; short costal cartilages terminate in abdominal wall muscle * Head articulates with demifacets of two adjacent vertebral bodies; neck located between head and tubercle of each rib;tubercle articulates with vertebral transverse process * Body: Longest part of each rib * Angle: Most posterior part * Costal groove on inner surface of inferior border; accommodates intercostal neurovascular bundle The typical rib has a head, neck, shaft and tubercle that projects posteriorly from the lateral end of the neck. * The head: is bevelled by two articular facets that articulates with its own vertebra and the vertebra above. Each makes a synovial joint. The cavities are separated by a ligament attached to the ridge on the head and to the intervertebral disc. * The neck: is flatterned with a sharp crest forming the upper border. The two laminae for the superior costotransverse ligament are attached here. * Tubercle has two facet. ** Medial smooth facet forms a synovial joint with the transverse process of its own vertebra. ** Lateral rough facet gives attachment to the lateral costotransverse ligament. * The shaft: the main body of the rib, slopes down and back to the angle '''(where the ribs make a turn) and whence twists forward. The head of the ribs lie at higher level than their anterior ends. The upper border of the rib is blunt and provide attachment to external and internal intercostal muscles.The anterior end of the rib is excavated into a concave fossa which is plugged by costal cartilage, Normal variant: * Cervical rib – fibrous or osseous. May articulate with rib 1. * Lumbar rib * Fused rib 1 and rib 2 * Hypoplastic ribs * Rib agenesis (usually rib 1) * Shortened rib 1 * Rib 12 absence The first rib is the most superior of the twelve ribs. It is an atypical rib and is an important anatomical landmark and is one of the borders of the superior thoracic aperture. Compared to a typical rib, first rib is short and thick and it has single articular facet for the costovertebral joint. The first rib has a head, neck and shaft but lacks a discrete angle. The neck slopes upwards, backwards and laterally to the tubercle. The plane of the shaft is 45 degree to horizontal and tubercle is the most posterior and highest part of the rib. * The '''head is small and carries single facet for synovial joint with the T1. * The transverse tubercle of the neck medially has a convex facet for the first transverse process and laterally, it receives the lateral costotransverse ligament. * The shaft is indented superiorly by the groove for the subclavian artery, which contains the lowest brachial plexus trunk as well as the subclavian artery. Between this and the transverse tubercle lies the scalene medius. Anterior to the groove, the inner border is projected into a small spur called the scalene tubercle where the scalenus anterior attaches. Anterior to the scalene tubercle is another groove for the subclavian vein. There is no costal groove on its inferior surface. The anterior end of the shaft expands into a concavity for the first costal cartilage. Articulations * costovertebral joint: articular facet on head of the rib with single articular facet * costotransverse joint: articular facet on transverse tubercle with transverse process of T1 * costochondral joint: distal shaft with first costal cartilage Attachments * anterior scalene muscle: scalene tubercle * middle scalene muscle: between groove for the subclavian artery and transverse tubercle * intercostal muscles: from the blunt outer border of the first rib * subclavius muscle: arises from distal shaft and first costal cartilage * first digitation of the serratus anterior muscle: between the transverse tubercle and the groove for subclavian artery. * parietal pleura: from the inner border * costoclavicular ligament: anterior to the groove for the subclavian vein Relations * superiorly: lower trunk of the brachial plexus; subclavian vessels; clavicle * inferiorly: the first intercostal vessels and nerves, parietal pleura, external and intercostal muscles. * internally: sympathetic trunk; superior intercostal artery; first posterior intercostal vein (medial to lateral over the head), ventral T1 nerve root, pleural layers of the dome, suprapleural membrane in front of the subclavian groove * externally: serratus anterior, pectoralis major Ossification: * Primary center of ossification at 8/40 * Secondary center in the head and the tubercle appear at 14 years and fuses at 25 years. Variant anatomy * ossesous or fibrous articulation or fusion with a cervical rib * bifid (forked) rib * rudimentary (hypoplastic) rib: most commonly the first rib (0.2%) * pseudoarthrosis of the first rib (0.1%)